MathDB
There exists a finite configuratio- Iran NMO 2005 - Problem4

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September 21, 2010
inductioncombinatorics proposedcombinatorics

Problem Statement

We have a 2×n2\times n rectangle. We call each 1×11\times1 square a room and we show the room in the ithi^{th} row and jthj^{th} column as (i,j)(i,j). There are some coins in some rooms of the rectangle. If there exist more than 11 coin in each room, we can delete 22 coins from it and add 11 coin to its right adjacent room OR we can delete 22 coins from it and add 11 coin to its up adjacent room. Prove that there exists a finite configuration of allowable operations such that we can put a coin in the room (1,n)(1,n).